LEDs have low power consumption, high efficiency, quick reaction time, long lifetime, and the absence of toxic elements such as mercury during manufacturing. Due to those advantages, traditional light sources are gradually replaced by LEDs.
A conventional LED lamp includes a substrate and a plurality of LEDs arranged on the substrate. The LEDs are usually densely arranged in array on the top surface of the substrate. However, the conventional LED generally generates a smooth round light field with a radiation angle of 90 degrees (−45 degrees to 45 degrees), wherein the light at a center of the conventional LED (i.e., 0 degree) is relatively great and the light at a periphery of the conventional LED is relatively poor. Such that, light emitted by the LED lamp including the conventional LEDs densely arranged on the substrate has a small radiation angle and is unevenly distributed, and thereby a whole light output of the LED lamp is barely satisfactory for illumination.